Electrochemical cells, or batteries, are commonly used as electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized. The cathode contains an active material that can be reduced. The anode active material is capable of reducing the cathode active material. A separator is disposed between the anode and the cathode. These components are contained within a can, or housing, that is typically made from metal.
When a battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the anode and cathode to maintain charge balance throughout the battery during discharge.
Batteries that include an indicator for visually displaying the condition, such as the state of charge, of the battery are known. Known indicators include, for example, electrochromic materials in electrical contact with the battery and thermochromic materials in thermal contact with a resistive element that is adapted to be connected across the battery. Electrochromic materials are materials that change color or transparency when subjected to electrical charge. Thermochromic materials are materials that change color or transparency when subjected to temperature change.
The known indicators typically require a consumer to physically interact with the indicator in order for the battery-related information to be displayed. A thermochromic indicator, for example, may include a resistor that is connected in series with the battery to form a circuit during voltage measurement. A switch must be present within the circuit to break electrical connection from the indicator to the battery when the indicator is not in use. The battery will prematurely discharge if the thermochromic indicator is in permanent electrical contact with the battery since a leakage current will be flow from the battery through the thermochromic indicator. Known electrochromic indicators will also suffer from issues associated with battery leakage current, similar to that of thermochromic indicators, without the presence of a switch within the indicator circuit. In addition, consumers with, or without, dexterity issues may find it difficult to operate the switch within the indicator. The switch generally includes at least one, and more often two, press-points that must be engaged to close the circuit. The press-points are typically very small; may be hard to see; and may be difficult to press. The known indicators are also sensitive to the amount of force with which the press-point(s) are closed. The condition of the battery that is displayed, if a condition is displayed at all, may be affected by the sensitivity and thus the accuracy of the indicator may be adversely affected.
Known indicators may also be permanently connected to the battery so that consumer interaction is not needed to activate the battery condition indicator. The known indicators of this type, however, typically include a distinct indicator electrode and a distinct counter electrode within the construction of the indicator. The inclusion of two electrodes within the indicator occupies space and increases the complexity of manufacturing the indicator. In addition, the additional components increases the overall cost of manufacturing the indicator.
The present invention overcomes the problems associated with the known indicators by employing a battery tester comprising an electrochemically generated display that is in permanent electrical connection with the battery. Consumer interaction to display the condition or state of charge of the battery is not needed. The accuracy of the indicator is not adversely affected by the operation of a switch since no consumer interaction is needed to activate the indicator. The affects of parasitic discharge are minimized within the battery condition indicator of the present invention and the useful capacity of the battery is minimally reduced over an extended period of storage. The indicator of the present invention is also simplistic in design and is less costly with respect to known indicators to manufacture.